We present results of the electronic structure and stability of calcium coverings on C60 using a linear combination of atomic orbitals and the local density functional approximation. Calculations on CaxC60 with x=12, 20 and 32 show partial charge transfer from calcium atoms to C60 and hybridization of the calcium and fullerene states. This leads to (i) a large binding energy of Ca on C60 which decreases with an increasing coverage and (ii) formation of a metallic shell on C60. The large abundance of the Ca32C60 complex is shown to be due to geometric factors in agreement with experiments. {\textcopyright} 2001 Elsevier Science B.V.